Hashimoto Encephalopathy

Hashimoto encephalopathy, also called steroid responsive encephalopathy associated with autoimmune thyroiditis (SREAT), is an encephalopathy with anti thyroid antibodies that responds to immunotherapy.

• Rare (2 per 100,000); women predominate; peak age 40 to 50, can occur at any age.

• Anti thyroid peroxidase (or thyroglobulin) antibodies are present in high titres but are likely markers rather than pathogenic.

• Thyroid function is usually normal or mildly abnormal.

• Diagnosis of exclusion.

• Relapsing remitting or progressive encephalopathy: confusion, cognitive decline, psychosis, hallucinations, seizures (including status epilepticus), myoclonus, tremor, stroke like episodes, headache.

• Ataxia, sleep disturbance, depression.

• Fluctuating course, subacute onset.

• Elevated anti TPO and/or anti thyroglobulin antibodies (any titre; typically high); TSH and free T4.

• CSF: elevated protein, mild pleocytosis, oligoclonal bands; EEG: diffuse slowing, triphasic waves.

• MRI normal in 50%, or non specific T2/FLAIR white matter changes.

• Exclude infection, autoimmune encephalitis with neuronal antibodies (NMDA, LGI1), Creutzfeldt-Jakob disease, metabolic, toxic and neoplastic causes, vasculitis.

• Clinical response to steroids supports diagnosis.

• Methylprednisolone 1 g IV daily for 3 to 5 days, then prednisolone 1 mg/kg daily with slow taper over 3 to 6 months or more; response in 90% (days to weeks).

• Refractory or relapsing disease: IVIG 2 g/kg over 5 days, plasma exchange, then steroid sparing agents (azathioprine 2 mg/kg, mycophenolate 1 g twice daily, methotrexate 15 to 25 mg weekly, rituximab, cyclophosphamide).

• Antiseizure medication for seizures; levetiracetam preferred.

• Thyroid replacement if hypothyroid (levothyroxine 1.6 micrograms/kg) or antithyroid drugs if hyperthyroid.

• Bone protection, Pneumocystis prophylaxis on prolonged immunosuppression.

• Relapse is common on taper; follow clinically and with antibodies.